Constant velocity joints are typically employed in automotive axial drive shafts, and especially in front-wheel-drive vehicles between the transaxle differential and the driving wheel. They are used to transmit torques at various speeds, angles and telescopic positions between a first shaft and second shaft.
There are many types of CV joints. One CV joint configuration includes a rotatable first shaft that has an axle portion and a pocket end disposed at an end of the axle portion. The first shaft is rotatable about a first longitudinal axis. The pocket end is disposed within a joint housing that is disposed on an end of a second shaft. The second shaft is rotatable about a second longitudinal axis. The joint housing includes a plurality of grooves disposed within a central bore and extending along the second longitudinal axis. The pocket end includes a diameter transverse to the first longitudinal axis that is greater than a diameter of the axle portion of the first shaft. The pocket end defines a plurality of semi-spherical pockets that are circumferentially and radially disposed about the first longitudinal axis in a configuration that is complementary relative to the plurality of grooves. As such, the number of pockets is equal to the number of grooves. The CV joint includes a plurality of spherical drive balls with one drive ball rotatably disposed within each pocket and corresponding groove. The pocket end and first shaft are moveable and may be articulated or stroked axially relative to the second shaft. As the CV joint is articulated (i.e., as the second shaft is moved relative to the first shaft by axial stroking or angulation) the drive balls roll back and forth along the grooves and rotate within the pockets.
A common axle shaft configuration for rear wheel drive drivetrain systems includes the use of stroking CV joints, as described above, to provide both an inboard and an outboard CV joint associated with a common axle shaft. In this configuration, the axle shaft is capable of floating between the inboard CV joint and the outboard CV joint because neither of the inboard CV joint nor the outboard CV joint fixes the axial position of the axle shaft. As such, the axle shaft is free to float inwards or outwards toward the inboard CV joint or the outboard CV joint, respectively. The axle shaft may float into one of the inboard CV joint or the outboard CV joint a stroke distance, the stroke distance being the maximum amount of axial travel or stroke permitted by the CV joint. When the axle shaft is in a fully-stroked position relative to one of the inboard CV joint or the outboard CV joint, the range of articulation for that CV joint is reduced and/or limited. This is because the axle shaft usually includes a flat end surfaces located adjacent to the pockets at the pocket ends upon which the axle shaft may rest against the housings (i.e., the axle shaft may bottom out against one of these flat surfaces). Accordingly, the flat surface prevents or hinders articulation of the axle shaft relative to the housing when the axle shaft is in the fully-stroked position. If the axle shaft is in the fully-stroked position and is required to articulate an amount beyond the small range of angular movement that the joint is capable of in this position, the range of articulation may be exceeded and joint failure or damage is possible.
In addition to the limitation described above, the stroking CV joints described above that have a flat distal end are restricted to operating within a given range of articulation. If the first shaft and the second shaft articulate beyond this range of articulation, then it is possible for one or more of the drive balls to become dislodged from within its pocket. Once dislodged, the drive ball becomes trapped within the housing, between the housing and the pocket end, thereby causing the CV joint to fail. Other different styles of CV joints prevent over-articulation by utilizing an outer edge of the housing as a limiter against which the second shaft abuts, thereby limiting the range of articulation. However, in the inexpensive type of stroking CV joint described above, the geometric shape of the various components render this solution cost prohibitive, and thereby impracticable.
Accordingly, there remains a need to limit the range of articulation in ball-in-socket stroking CV joints, such as described above, in order to prevent ejection of one or more of the drive balls, as well as a need to provide a greater range of articulation of these joints when they are fully stroked inwardly into the housing.